1. Field of the Invention
The present invention relates to a hose rupture control valve unit (often called a hose rupture valve) which is provided in a hydraulic machine, such as a hydraulic excavator, for preventing a drop of the load upon rupture of a cylinder hose.
2. Description of the Prior Art
In a hydraulic machine such as a hydraulic excavator, there is a need for preventing a drop of the load even if a hose or steel pipe for supplying a hydraulic fluid to a hydraulic cylinder, serving as an actuator for driving a load, e.g., an arm, should be ruptured. To meet such a need, a hose rupture control valve unit (often called a hose rupture valve) is provided in the hydraulic machine. FIG. 8 is a hydraulic circuit diagram showing a typical conventional hose rupture control valve unit, and FIG. 9 shows a sectional structure of the hose rupture control valve unit.
Referring to FIGS. 8 and 9, a hose rupture control valve unit 200 comprises a housing 204 provided with two input/output ports 201, 202 and a reservoir port 203. The input/output port 201 is directly attached to a bottom port of a hydraulic cylinder 502, the input/output port 202 is connected to one of actuator ports of a control valve 503 via a hydraulic line (hose) 505, and the reservoir port 203 is connected to a reservoir 509 via a drain line (hose) 205. Within the housing 204, there are provided a main spool 211 operated with a pilot pressure supplied as an external signal from a manual pilot valve 508, a check valve 212 for fluid supply, a poppet valve body 214 controlled by a pilot portion 213 which is provided in the circumference of the main spool 211, and an overload relief valve 215 for releasing an abnormal pressure.
In the conventional hose rupture control valve unit 200 having the above-described construction, supply of a hydraulic fluid to the bottom side of the hydraulic cylinder 502 is effected by supplying the hydraulic fluid from the control valve 503 to the bottom side through the fluid-supply check valve 212. Also, discharge of the hydraulic fluid from the bottom side of the hydraulic cylinder 502 is effected by operating the main spool 211 of the valve unit 200 with the pilot pressure as an external signal to first open the poppet valve body 214 controlled by the pilot portion 213 which is provided in the circumference of the main spool 211, and then open a variable throttle portion 211a also provided in the circumference of the main spool 211, thereby draining the hydraulic fluid to the reservoir 509 while controlling the flow rate of the hydraulic fluid.
The poppet valve body 214 is provided in series with respect to the main spool 211, and has the function (load check function) of reducing the amount of leakage in a condition of holding the load pressure on the bottom side of the hydraulic cylinder 502.
The overload relief valve 215 operates to drain the hydraulic fluid and prevent hose rupture in the event an excessive external force acts on the hydraulic cylinder 502 and the hydraulic pressure supplied to the bottom side of the hydraulic cylinder 502 is brought into a high-pressure level.
Also, if the hydraulic hose 505 leading from the control valve 503 to the input/output port 202 should be ruptured, the check valve 212 and the poppet valve body 214 are closed to prevent a drop of the load borne by the hydraulic cylinder 502. At this time, by operating the main spool 211 with the pilot pressure from the manual pilot valve 508 and adjusting an opening area of the variable throttle portion 211a, it is possible to slowly contract the hydraulic cylinder 502 under action of the weight of the load itself and to move the load to a safety position.
Numerals 507a and 507b denote main relief valves for limiting a maximum pressure in the circuit.
Further, JP, A, 3-249411 discloses a hose rupture control valve unit utilizing a proportional seat valve to reduce an overall size of the valve unit. FIG. 10 shows the disclosed hose rupture control valve unit.
Referring to FIG. 10, a hose rupture control valve unit 300 comprises a housing 323 provided with an input port 320, a work port 321 and a reservoir port 322. The input port 320 is connected to one of actuator ports of a control valve 503, the work port 321 is connected to a bottom port of a hydraulic cylinder 502, and the reservoir port 322 is connected to a reservoir 509 via a drain line (hose) 205. Within the housing 323, there are provided a check valve 324 for fluid supply, a proportional seat valve 325, an overload relief valve 326, and a pilot valve 340. The pilot valve 340 is operated with a pilot pressure supplied as an external signal from a manual pilot valve 508 (see FIG. 8), and the proportional seat valve 325 is operated with the operation of the pilot valve 340. The overload relief valve 326 is incorporated in the proportional seat valve 325.
Supply of a hydraulic fluid to the bottom side of the hydraulic cylinder 502 is effected by supplying the hydraulic fluid from the control valve 503 to the bottom side through the fluid-supply check valve 324 of the valve unit 300. Also, discharge of the hydraulic fluid from the bottom side of the hydraulic cylinder 502 is effected by operating the pilot valve 340 of the valve unit 300 with the pilot pressure, as an external signal, to open the proportional seat valve 325, thereby draining the hydraulic fluid to the reservoir 509 while controlling the flow rate of the hydraulic fluid. The proportional seat valve 325 has the function (load check function) of reducing the amount of leakage in a condition of holding the load pressure on the bottom side of the hydraulic cylinder 502.
The overload relief valve 326 operates to open the proportional seat valve 325 for draining the hydraulic fluid and preventing hose rupture in the event an excessive external force acts on the hydraulic cylinder 502 and the hydraulic pressure supplied to the bottom side of the hydraulic cylinder 502 is brought into a high-pressure level.
Also, if a hydraulic line (hose) 505 leading from the control valve 503 to the input port 320 should be ruptured, the check valve 324 and the proportional seat valve 325 are closed to prevent a drop of the load borne by the hydraulic cylinder 502. At this time, by operating a spool 341 of the pilot valve 340 with the pilot pressure and adjusting an opening area of the proportional seat valve 325, it is possible to slowly contract the hydraulic cylinder 502 under action of the weight of the load itself and to move the load to a safety position.